The frequency of electrocardiographic Q-wave formation and the relation of Q wave and QRS score to regional and global left ventricular (LV) performance were determined in 131 patients with acute myocardial infarction (AMI) receiving thrombolytic therapy. Thrombolytic therapy was successful in reperfusing the occluded infarct artery in 100 patients and was unsuccessful in 31. The number of patients who had 1 or more Q waves (88 vs 87%) and 2 or more Q waves (70 vs 74%) was similar. In contrast, normal wall motion was significantly more common in the infarct area in patients in whom reperfusion was successful (42 vs 15%, p less than 0.05). Total QRS scores were similar in patients in whom reperfusion was successful and in those in whom it was not (6.0 +/- 3.2 vs 6.4 +/- 4.2). Despite similar QRS scores, successfully treated patients had significantly higher LV ejection fraction (53 +/- 13% vs 46 +/- 15%, p less than 0.05). Thus, Q-wave formation after successful thrombolytic therapy for AMI is common but does not faithfully reflect regional or global LV performance. Electrocardiographic analysis alone is not a reliable method to assess efficacy of reperfusion therapy.